THE NAUTILUS. 33 
Beyond question this is the most philosophical and compre- 
hensive study of the Naiad fauna of this country (or any other, 
for that matter) that has yet appeared, The elaborate compila- 
tion of all the records of the Pennsylvania fauna supplemented 
by the extensive and intensive collections made by the author 
leave but little to be added by later investigations, and the wealth 
of anatomical and ecological details will be a revelation to those 
who have not kept au courant with the trend of modern methods 
of scientific research. The excellent keys of both generic and 
specific characters add much to the practical value of the paper 
to the student. 
In addition to the details of local distribution, the author has 
supplied complete summaries of the general distribution of each 
of the species treated so far as given in the literature, supple- 
mented by the material in the Carnegie Museum; and his com- 
ments thereon at once reveal the inadequacy of our present 
knowledge to furnish a proper basis for an accurate and truly 
scientific study of the fundamental facts of the origin and dis- 
tribution of the Naiad fauna of the country and raise many 
pertinent questions, which can not well be touched upon in this 
review, but which will undoubtedly excite discussion and in- 
crease the interest of American students in their local faunas. 
This study of the fauna of Pennsylvania will be a model for 
others to imitate for many years to come. 
The Naiad fauna of Pennsylvania as recognized by the author 
includes 58 species and 21 varieties. Of these seven species be- 
long to the Atlantic fauna and two species and one variety, 
while characteristic of the Atlantic drainage, are clearly deriva- 
tives from western species. The remainder belong to the Mis- 
sissippian fauna of Simpson. 
The systematic arrangement of the various groups represented 
in the fauna is that which has been elaborated by the author in 
previous papers and represents the modern tendency to multiply 
genera. How far this is really advisable is a subject for serious 
consideration as practically the same results, so far as syste- 
matics are concerned, can be obtained the use of subgenera, 
which will sufficiently indicate the differences, while retaining 
not only the familiar names, but also the larger relationships, 
